Four collaborative studies are proposed for execution in San Francisco in New York. Research will be conducted that examines: (1) Knowledge of AIDS risk factors, and participation in risky behaviors, among intravenous drug users (IVDUs). (2) Seroprevalence of antibodies to the HTLV-III retrovirus. (3) The psychological impact of knowledge of seropositivity. (4) Factors that may mediate successful dissemination and utilization of AIDS risk-reduction messages for specific sub-populations of IVDUs. Approximately 1,200 IVDUs will be examined each year in San Francisco (800 from treatment programs and 400 out-of-treatment individuals). About 400 IVDUs per year will be examined in New York.